Ireland to England 13 days

Are you crazy? You know the answer already.

Whereabouts in England to whereabouts in Ireland - most people would fly.

Maybe it would help if you expanded on what locations you mean when you say Ireland and England.

I've done a 14 day tour of Ireland and didn't scratch the surface.

If you mean Dublin, London and Paris then you might be able to do it with Dublin 4 nights (just 3 full days but no time to visit the country side except for perhaps a day trip), London 5 nights and Paris 4 nights. I see your last name is probably Irish so did you want to include travel to where relatives emigrated from?

Are you counting your travel days from the US? That takes 2 days off at the start as many people don't get much quality sightseeing done on their jet-lagged arrival day. Your departure day you'll not get anything done except getting to the airport. You'll lose at least two 1/2 days for your transits between Dublin -> London and London -> Paris.

You'll want to fly from Dublin to London or wherever your one destination is in England.

Using the Eurostar is excellent for transportation between London and Paris. You'll book your tickets on www.eurostar.com It's not really referred to as the "Chunnel".

I don't see time in there for Wales.

You can get a rail+ferry ticket for the journey from London to Ireland, by a route that is through Wales - or break that journey somewhere in Wales (Abergavenny, perhaps?) en route. (Or in the reverse direction.)
The Man in Seat 61 is, as always, very helpful with the details.

With just 13 days, you'll need to winnow out the extras and focus on your top priorities. Say you fly open jaw US-Dublin, then Dublin-London, take the Eurostar to France and fly Paris-US. I'm counting Day 1 as your arrival day, and Day 13 as your departure day.

Day 1, 2, 3 Dublin
Day 4 (fly Dublin-London), 5, 6, 7, 8 London and surrounding day trips
Day 9 Eurostar
Day 10, 11, 12 Paris with possible day trip e.g. Versailles or Fontainbleau
Day 13 go to airport

If you really wanted to take the ferry-train combo from Ireland through Wales to London, then count Day 4 as a travel day.
It's a lot of hopping around to visit 3 countries in 13 days, but not totally insane provided you realize going in that you will only scratch the surface of each destination.

Not trying to be snarky, but almost always when someone on this board asks "are we crazy" the answer is "yes". I don't think Ireland and England are that easy to combine into a single trip, because the places you really want to see in Ireland are in the country. Likewise England, as wonderful as London is, you really want to see some of the smaller towns too. Three or four countries in 13 days is just too much. That amount of time lends itself to a single-country itinerary. Two countries at most. You could do London, Paris, and some England outside of London in this time. Or Ireland (for example County Clare, Kilkenny, Dublin) and London. I suggest getting some guidebooks from the library, watching some Rick Steves videos on YouTube, and narrowing it down.

Thank you for all your input. This trip is at its baby phase right now, so you have given us some options. July is when we are going. Thinking we need to stick to just England and all that it has to offer (city and countryside) with a possible jump to Wales since my husband has Welsh (as well as Irish) heritage.
We’ve been told by people who have traveled and lived overseas that a trip using Eurostar is easy if we do decide to experience Paris before going back home?